We can use the following formula to convert Farads to Amp hours(Vmin + Vmax)/2 * F / 3600 = AhVmin & Vmax is the upper and lower voltage. This is the voltage range that your device has to work in. As capacitors "run down" and need charging, their voltage drops, so we have to allow for that. If we assume that we want to power a 3 volt radio, we can guess that it should work happily between 3.5 volts and 2.5 volts. That's what the first part of the calculation allows for;In our example, (Vmin + Vmax)/2 would be (3.5v + 2.5v) / 2 equals 3 volts.

In the rest of the calculation, F - Farads and3600 - coulomb, a unit of electrical measure. One amp hour = 3,600 CAh - Amp hours ( 1000 mAh = 1Ah)So we now have 3 * F / 3600 = AhLet's say we can get hold of a 3.5 volt 100 F super-capacitor. Using 3 * 100 / 3600 = Ah,we could expect it to power a device drawing 0.083 amps, or 83 milliamps, for one hour.What if this wasn't enough? What if we wanted a 3 volt capacitor to power a 3 volt device which drew 250mA for one hour?We can use the formula "current in amps * 3600 / voltage = capacitance needed in Farads" to find out how big the capacitor needs to be. In this example0.25 * 3600 / 3 = 300 FThe capacitor would need to be 3v 300F to power a 3 volt device drawing 250mA for 1 hour. Ideally, you should have a capacitor of slightly more than 3 volts to allow for the voltage drop mentioned above.

But when you say (Vmax + Vmin), you must mean minus not plus. Vmin will be a parameter which reduces the useful overall power capacity of the cap.

Paul,

All what the you are trying to do here is find the mid-range or average working voltage. Remember it is a value you choose based on what you need as the min voltage for the equipment you are going to connect to the Cap.To can also find the same average by, do a minus, then divide by 2 then add to Vmin.Sure the higher Vmin is, the smaller your working range becomes. The same as with a battery. Although with a battery, this value is usually set by the battery type, the lowest discharge voltage before the battery becomes irrecoverable damaged.